Field of the Invention
This invention relates to color cathode ray picture tubes, and is addressed specifically to an apparatus and process for use in the manufacture of tubes having a flat tension mask.
In U.S. Pat. No. 4,828,523 to Fendley et al, of common ownership herewith, a welding apparatus is described and claimed which utilizes a laser beam for welding an in-process foil shadow mask to a faceplate-mounted, frame-like shadow mask support structure secured to the inner surface of an in-process faceplate. The apparatus comprises mapping means for creating a map of the mask-receiving surface of the support structure. Means are included for moving the laser beam to follow the map in welding relationship to the mask-receiving surface, and controlling the beam to weld the mask to the support structure. Following the welding process, the border of the mask is severed by the same beam.
Although mask-severing by laser beam has proved to be production effective, there is a liability in that any overshoot and/or reflection of the high-power beam in severing the mask can damage the material of the mask-support structure and/or the glass of the faceplate. As a result, it has been necessary to build beam-shielding means into the mask-support structure to deflect the severing beam. Alternately, a separate beam shield must be manually emplaced in the path of the beam before each welding operation. Another disadvantage of severing the border for a mask by laser beam is that beam, in impacting the faceplate or the shielding means, tends to produce artifacts in the form of particles and other residue that can occlude the nearby apertures in the centrally located screening area.
The "mask-tensing fixture," as it is termed in the present application, is described and claimed in U.S. Pat. No. 4,790,786 of common ownership herewith. The fixture, which is referred to as a "factory fixture frame" in the cited patent, provides for mounting an in-process shadow mask during photoexposure of an in-process faceplate in a lighthouse. The frame comprises generally rectangular frame means and quick-release mechanical mask-retaining means for temporarily and removably supporting an in-process shadow mask in tension. By virtue of this fixture, an in-process shadow mask can be precisely registered and re-registered with a lighthouse and an in-process faceplate for the photoexposure of the in-process faceplate while retaining the in-process shadow mask in tension, all as described in the '786 patent.